Coating composition for protecting dazzling effect

ABSTRACT

The present invention relates to an antiglare coating composition, and more particularly to an antiglare coating composition comprising an acrylate binder resin, fine particles whose refractive index varies between 0.2 to 0.5 from the refractive index of the binder resin and whose average particle size ranges from 0.05 to 1 μm, and fine particles whose refractive index varies between 0.1 and whose average particle size ranges from 0.5 to 3 μm. A coating composition of the present invention has a superior antiglare effect, reduced image distortion, high contrast, and enhanced image clarity when applied to a high-resolution display by scattering and inducing internal diffusion of light.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an antiglare coating composition, andmore particularly relates to an antiglare coating composition having asuperior antiglare effect, reduced image distortion, high contrast, andenhanced image clarity when applied to a high-resolution display.

(b) Description of the Related Art

With the advent of the information society, various sizes and types ofdisplays are being developed for TVs, notebook computers, PCs, mobilephones, clocks, picture frames, etc. However, these displays haveseveral problems when exposed to an external light such as a fluorescentlight or sunlight. For instance, when an incident light is reflectedfrom a surface of the display in one direction, the image contrastreduced and the reduced image contrast cause eye fatigue or headaches.

Conventionally, to solve the above-mentioned problems, method ofscattering eternal light has been used by forming an uneven surface.Japan Patent Publication Nos. Sho 59-58036, Hei 6-18706, and Hei9-127312 disclose methods of diffusing reflected light by insertingcoagulated fine particles such as silica or polymer beads in thethermosetting resin to provide an uneven surface. Furthermore, embossingtreatment method of the coated surface has been reported.

While these methods superior antiglare effect, these methods also givesrise to serious problems of image distortion when applied to ahigh-resolution display. Japan Patent Publication Nos. Hei 7-181306 andHei 10-20103 disclose the antiglare film having fine surface roughnesswhich is applicable to a high-resolution display. Although these methodsreduced image distortion, the problem of decrease in contrast still didnot be solved.

Therefore, the development of an antiglare coating composition having asuperior antiglare effect, reduced image distortion, high contrast, andenhanced image clarity when applied to a high-resolution display isgreatly needed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an antiglare coatingcomposition having a superior antiglare effect, reduced imagedistortion, high contrast, and enhanced image clarity when applied to ahigh-resolution display.

In order to attain the object, the present invention provides anantiglare coating composition having a superior antiglare effect for adisplay comprising:

-   -   a) 100 wt % of an acrylate binder resin;    -   b) 2 to 30 wt % of fine particles having an average particle        size of 0.05 to 1 μm, wherein the refractive index of the fine        particles varies between 0.2 to 0.5 from the refractive index of        the acrylate binder resin; and    -   c) 1 to 20 wt % of fine particles having an average particle of        0.5 to 3 μm, wherein the refractive index varies within 0.1 from        the refractive index of the acrylate binder resin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventors worked to develop a coating composition having asuperior antiglare effect, reduced image distortion, high contrast, andenhanced image clarity when applied to a high-resolution display. Indoing so, they discovered that when the fine particles whose refractiveindex varies between 0.2 to 0.5 and between 0.1 from the refractiveindex of a binder resin are added to the binder resin, the coatingcomposition shows superior antiglare effect, reduced image distortion,superior contrast, and distinct images.

Because of the large difference in refractive indices of coating layerand atmosphere, the image transmitted from display is greatly refractedin the outermost surface of coating layer, and interference between thetransmitted images arises. However, inside of the film, the differencein refractive indices of the filler and the matrix is smaller than thedifference in refractive indices of the coating layer and theatmosphere. The coating composition of the present invention should havea coated film with average surface roughness of 0.1 to 0.3 μm to provesuperior antiglare effect with minimum image distortion.

In addition, control of internal and surface light diffusion isimportant for a high-resolution display. Particularly, when haze byinternal scattering is between 15 to 40 and haze by internal scatteringis less than 15, the coated film shows superior antiglare effect,minimum image distortion. Internal scattering is influenced by thecontent and size of fine particles whose refractive indices vary between0.2 to 0.5 from the refractive index of the binder, while surfacescattering is determined by the surface roughness. Therefore, two typesof fine particles are required.

The present invention is characterized by a coating compositioncomprising an acrylate binder resin, fine particles whose refractiveindex varies between 0.2 to 0.5 from the refractive index of the binderand the average particle size of the fine particles size ranges from0.05 to 1 μm, and fine particles whose refractive index varies between0.1 from the refractive of the binder and average particle size of thefine particles size ranges from 0.5 to 3 μm.

The fine particles whose refractive index varying between 0.2 to 0.5from the refractive index of the binder and whose average particle sizeranging from 0.05 to 1 μm, and the fine particles whose refractive indexvarying between 0.1 from the refractive index of the binder and averageparticle size ranging from 0.5 to 3 μm used in the present invention canbe selected from alumina (refractive index: 1.77), aluminum hydroxide(refractive index: 1.58), magnesium oxide (refractive index: 1.74),antimony oxide (refractive index: 2.18), or silica (refractive index:1.48).

It is preferable that the fine particles whose refractive index variesbetween 0.2 to 0.5 from the refractive index of the binder resin andwhose average particle size ranges from 0.05 to 1 μm are used at 2 to 30wt % for 100 wt % of the binder resin. If the average particle size ofthe fine particles is smaller than 0.05 μm, light diffusion effectsdisappear. Otherwise, if the average particle size exceeds 1 μm, lightblurring increases.

Also, it is preferable that the fine particles whose refractive indexvaries within 0.1 from the refractive index of the binder resin are usedat 1 to 20 wt % for 100 wt % of the binder resin. If the averageparticle size of the fine particles exceeds 3 μm, light blurringincreases.

Also, it is preferable that the acrylate binder resin used in thepresent invention comprises: i) up to 80 wt % of a reactive oligomer;ii) 10 to 100 wt % of a multifunctional monomer; and iii) up to 30 wt %of one or more bifunctional or monofunctional acrylates.

For the reactive oligomer, a urethane-modified oligomer, a polyesteroligomer, an epoxy oligomer, etc. having 2 to 6 functional groups can beused. It is used up to 80 wt % for 100 wt % of the acrylate binderresin. If its content exceeds 80 wt %, abrasion resistance and scratchresistance decreases.

For the multifunctional monomer, an acrylate having more than 3functional groups, such as dipentaerythritol hexaacrylate,pentaerythritol tetraacrylate, pentaerythritol triacrylate, andtrimethylene propyl triacrylate, can be used. It is used at up to 10 wt% for 100 wt % of the acrylate binder resin. If its content is less than10 wt %, abrasion and scratch resistance decrease.

The bifunctional or monofunctional acrylate and methacrylate decreasesviscosity of the coating solution and offers softness to the coatingfilm. Monofunctional acrylates like ethyl acrylate, butyl acrylate,isobonyl acrylate, octadecyl acrylate, 2-hydroxyethyl acrylate, etc.;monofunctional methacrylates like methyl methacrylate, butylmethacrylate, etc.; bifunctional acrylates like hexanediol diacrylate,dipropylene glycol diacrylate, triethylene glycol diacrylate,tripropylene glycol diacrylate, etc.; bifunctionalmethacrylates can beused. It is preferable that the bifunctional or monofunctional acrylateand methacrylate is used up to 30 wt % for 100 wt % of the acrylatebinder resin.

An initiator and a solvent are also added to the coating composition ofthe present invention.

For the initiator, a thermal initiator or a UV initiator can be used.For the thermal initiator, peroxides of azo compounds, such as benzoylperoxides and AIBN can be used. For the UV initiator, 1-hydroxycyclohexylphenyl ketone, benzyl dimethyl ketal,hydroxydimethylacetophenone, benzoin, benzoin methyl ether, benzoinethyl ether, benzoin isopropyl ether, benzoin butyl ether, etc. can beused. It is preferable that the initiator is used at 0.01 to 10 wt % for100 wt % of the binder resin.

The solvent is used to offer coatability and adhesion property. Alcoholslike methanol, ethanol, isopropanol, etc.; acetates like methyl acetate,ethyl acetate, butyl acetate, etc.; ketones like methyl ethyl ketone,methyl isobutyl ketone, acetone, etc.; cellusolves like methylcellusolve, ethyl cellusolve, butyl cellusolve, etc.; dimethylformamide; or tetrahydrofuran, etc can be used as the solvent. It ispreferable that the solvent is used at 10 to 200 wt % for 100 wt % ofthe binder resin.

A composition of the present invention may further comprise a levelingagent, a wetting agent, an antifoaming agent, etc. to offer otherproperties such as coatability.

A coating solution prepared by the present invention can be applied on avariety of matrices. For example, transparent films such as triacetylcellulose, polyester or Sheets such as polymethylmethacrylate (PMMA),polycarbonate (PC), etc. can be used. Antiglare coating composition ofthe present invention provide good results when the coating compositionis used for polarizers for LCDs, protection filters for RPTVs, eyeprotectors for PC users, etc.

A coating composition of the present invention is coated on a film byroll coating. Specifically, gravure coating, reverse gravure coating,comma coating, reverse comma coating, rib coating, wire bar coating,etc. can be used for films. For sheets, dip coating, spray coating, flowcoating, spin coating, etc. can be used. Preferably, the thickness ofthe coating film ranges from 1 to 20 μm, depending on the field ofapplication. The coated matrix is pre-dried in oven at 50 to 80° C. toremove the solvent, and then hardened with a UV curing machine. It ispreferable that the UV irradiation amount ranges from 400 to 2000mJ/cm².

Hereinafter, the present invention is described in more detail throughExamples and Comparative Examples. However, the following Examples areonly for the understanding of the present invention, and the presentinvention is not limited by the following Examples.

EXAMPLES Example 1

10 wt % of alumina (AL-41 DBM-01; Sumitomo Chemical) having a refractiveindex of 1.77 and an average particle size of 1 μm as fine particles; 2wt % of 2-hydroxy cyclohexylphenylketone as a UV initiator; 20 wt % ofisopropyl alcohol, 20 wt % of ethyl acetate, and 20 wt % of butylcellusolve as a solvent; 0.3 wt % of a wetting agent (Tego 453; Tego);and 0.3 wt % of a leveling agent (BYK 300; BYK) were mixed in a binderresin containing 80 wt % of dipentaerythritolhexaacrylate (DPHA) and 20wt % of 2-hexanediolacrylate (2-HEA). The refractive index of the binderresin was 1.48.

The coating solution was dispersed with a milling machine, so that thefinal average particle size of the alumina was 0.4 μm.

7 wt % of silica having a refractive index of 1.48 and an averageparticle size of 1 μm was dispersed in 30 wt % of isopropyl alcohol and10 wt % of butyl cellusolve, and mixed with the coating solution toprepare a coating composition for preventing a dazzling effect.

Example 2

10 wt % of magnesium oxide (Premier) having a refractive index of 1.74and an average particle size of 4 μm as fine particles; 2 wt % of2-hydroxy cyclohexylphenylketone as a UV initiator; 20 wt % of isopropylalcohol, 20 wt % of ethyl acetate, and 20 wt % of butyl cellusolve as asolvent; 0.3 wt % of a wetting agent (Tego 453; Tego); and 0.3 wt % of aleveling agent (BYK 300; BYK) were mixed in a binder resin containing 80wt % of dipentaerythritolhexaacrylate (DPHA) and 20 wt % of2-hexanediolacrylate (2-HEA). The refractive index of the binder resinwas 1.48.

The coating solution was dispersed with a milling machine, so that thefinal average particle size of the alumina was 0.6 μm.

7 wt % of silica having a refractive index of 1.48 and an averageparticle size of 1 μm was dispersed in 30 wt % of isopropyl alcohol and10 wt % of butyl cellusolve, and mixed with the coating solution toprepare a coating composition for preventing a dazzling effect.

Comparative Example 1

10 wt % of silica having a refractive index of 1.48 and an averageparticle size of 1 μm as fine particles; 2 wt % of 2-hydroxycyclohexylphenylketone as a UV initiator; 50 wt % of isopropyl alcohol,20 wt % of ethyl acetate, and 30 wt % of butyl cellusolve as a solvent;0.3 wt % of a wetting agent (Tego 453; Tego); and 0.3 wt % of a levelingagent (BYK 300; BYK) were mixed in a binder resin containing 80 wt % ofdipentaerythritolhexaacrylate (DPHA) and 20 wt % of 2-hexanediolacrylate(2-HEA). The refractive index of the binder resin was 1.48.

Comparative Example 2

10 wt % of aluminum hydroxide having a refractive index of 1.58 and anaverage particle size of 1 μm, and 7 wt % of silica having a refractiveindex of 1.48 and an average particle size of 1 μm as fine particles; 2wt % of 2-hydroxy cyclohexylphenylketone as a UV initiator; 50 wt % ofisopropyl alcohol, 20 wt % of ethyl acetate, and 30 wt % of butylcellusolve as a solvent; 0.3 wt % of a wetting agent (Tego 453; Tego);and 0.3 wt % of a leveling agent (BYK 300; BYK) were mixed in a binderresin containing 80 wt % of dipentaerythritolhexaacrylate (DPHA) and 20wt % of 2-hexanediolacrylate (2-HEA). The refractive index of the binderresin was 1.48.

Test Example

Coating compositions prepared in Examples 1 and 2 and ComparativeExamples 1 and 2 were coated on a triacetyl cellulose film using a No. 5wire bar. The film was dried for 2 minutes in a 50° C. oven and hardenedwith 1 J/cm² of UV energy. Physical properties including gloss,haziness, internal haze, surface haze, transmittance, image clarity,sparkling, and black density of the coated film were tested. The resultsare shown in Table 1.

a) Haze and transmittance—HR-100 (Murakami) was used.

-   -   Internal haze was determined after attaching cellophane on the        film surface to remove roughness of the film. Surface haze was        obtained by subtracting the internal diffusion haze from the        total haze.

b) Image clarity—ICM-1 (Suga) was used. Distinctness of an image passingthrough 4 slits (0.125 mm, 0.25 mm, 0.5 mm and 2.0 mm) was added. Thehigher the sum, the better the distinctness.

c) Sparkling—The film was attached on a LCD module and sparkling wasobserved by human eye.

d) Black density—A black tape was attached on the back of the film, andblack density was evaluated with Macbeth RD198.

TABLE 1 Comparative Comparative Classification Example 1 Example 2Example 1 Example 2 Gloss (%) 62 59 59 60 Haze (%) 34.6 38.2 11 17.4Internal haze 30.5 33.0 0 3.4 Surface haze 4.1 5.2 11 14 Transmittance93.3 93.1 93.3 93.6 (%) Image clarity 177 163 100 108 Sparkling NoneNone Occurred Slightly occurred Black density 1.96 1.95 1.80 1.88

As seen in Table 1, the coating compositions of the present inventioncomprising a binder resin, fine particles whose refractive index varyingbetween 0.2 to 0.5 from the refractive index of the binder resin andwhose average particle size ranging from 0.05 to 1 μm, and fineparticles whose refractive index varying between 0.1 from the refractiveindex of the binder resin and whose average particle size ranging from0.5 to 3 μm (Examples 1 and 2) were superior in terms of transmittance,haze, image clarity, and sparkling to those of Comparative Examples 1and 2.

As explained above, an antiglare coating composition of the presentinvention has a superior antiglare effect, reduced image distortion,high contrast, and enhanced image clarity when applied to ahigh-resolution display by reducing surface scattering and inducinginternal diffusion of light.

1. An antiglare film comprising a substrate; and an antiglare coatingcomposition coated on the substrate, the antiglare coating compositioncomprising: a) acrylate binder resin; b) 2 to 30 wt % of inorganic fineparticles selected from a group consisting of alumina, aluminumhydroxide, magnesium oxide, antimony oxide, and silica having an averageparticle size ranging from 0.4 μm to less than 1 μm, wherein therefractive index of the fine particles varies between 0.2 to 0.5 fromthe refractive index of the acrylate binder resin, based on the weightof acrylate binder resin; and c) 1 to 20 wt % of inorganic fineparticles selected from a group consisting of alumina, aluminumhydroxide, magnesium oxide, antimony oxide, and silica, having anaverage particle size of 1 to 3 μm, wherein the refractive index of thefine particles varies within 0.1 from the refractive index of theacrylate binder resin, based on the weight of acrylate binder resin, andwherein the internal diffusion haze of the film ranges from 15 to 40 andsurface haze of the film is less than
 15. 2. The antiglare filmaccording to claim 1, wherein the substrate is selected from the groupconsisting of triacetyl cellulose, polyester film,polymethylmethacrylate (PMMA), and polycarbonate (PC).
 3. An antiglarecoated sheet coated with an antiglare coating composition, the antiglarecoating composition comprising: a) acrylate binder resin; b) 2 to 30 wt% of inorganic fine particles selected from a group consisting ofalumina, aluminum hydroxide, magnesium oxide, antimony oxide, andsilica, having an average particle size ranging from 0.4 μm to less than1 μm, wherein the refractive index of the fine particles varies between0.2 to 0.5 from the refractive index of the acrylate binder resin, basedon the weight of acrylate binder resin; and c) 1 to 20 wt % of inorganicfine particles selected from a group consisting of alumina, aluminumhydroxide, magnesium oxide, antimony oxide, and silica, having anaverage particle size of 1 to 3 μm, wherein the refractive index of thefine particles varies within 0.1 from the refractive index of theacrylate binder resin, based on the weight of acrylate binder resin, andwherein the internal diffusion haze of the film ranges from 15 to 40 andsurface haze of the film is less than
 15. 4. The antiglare filmaccording to claim 1, wherein the antiglare coating composition furthercomprises one or more additives selected from a group consisting of aleveling agent, a wetting agent, and an antifoaming agent.
 5. Theantiglare film according to claim 1, wherein the antiglare coatingcomposition comprises: a) acrylate binder resin comprising i) up to 80wt % of a reactive oligomer, ii) 10 to 100 wt % of a multifunctionalmonomer, and iii) up to 30 wt % of one or more bifunctional ormonofunctional acrylate and methacrylate; b) 2 to 30 wt % of inorganicfine particles selected from a group consisting of alumina, aluminumhydroxide, magnesium oxide, antimony oxide, and silica, having anaverage particle size ranging from 0.4 μm to less than 1 μm, wherein therefractive index of the fine particles varies between 0.2 to 0.5 fromthe refractive index of the acrylate binder resin, based on the weightof acrylate binder resin; c) 1 to 20 wt % of inorganic fine particlesselected from a group consisting of alumina, aluminum hydroxide,magnesium oxide, antimony oxide, and silica, having an average particlesize of 1 to 3 μm, wherein the refractive index of the fine particlesvaries within 0.1 from the refractive index of the acrylate binderresin, based on the weight of acrylate binder resin; d) 0.01 to 10 wt %of an initiator, based on the weight of acrylate binder resin; and e) 10to 200 wt % of a solvent, based on the weight of acrylate binder resin.6. The antiglare film according to claim 5, wherein the reactiveoligomer is one or more compounds selected from the group consisting ofa urethane-modified oligomer, a polyester oligomer, and an epoxyoligomer having 2 to 6 functional groups.
 7. The antiglare filmaccording to claim 5, wherein the multifunctional monomer is one or morecompounds selected from the group consisting of dipentaerythritolhexaacrylate, pentaerythritol tetraacrylate, pentaerythritoltriacrylate, and trimethylene propyl triacrylate.
 8. The antiglare filmaccording to claim 5, wherein the bifunctional or monofunctionalacrylate or methacrylate is one or more compounds selected from thegroup consisting of ethyl acrylate, butyl acrylate, isobornyl acrylate,octadecyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, butylmethacrylate, hexanediol diacrylate, dipropylene glycol diacrylate,triethylene glycol diacrylate, tripropylene glycol diacrylate, andmethacrylate.
 9. The antiglare film according to claim 5, wherein theinitiator is one or more compounds selected from the group consisting ofbenzoylperoxide, 1-hydroxy cyclohexylphenyl ketone, benzyl dimethylketal, hydroxydimethylacetophenone, benzoin, benzoin methyl ether,benzoin ethyl ether, benzoin isopropyl ether, and benzoin butyl ether.10. The antiglare film according to claim 5, wherein the solvent is oneor more compounds selected from the group consisting of methanol,ethanol, isopropanol, methyl acetate, ethyl acetate, butyl acetate,methyl ethyl ketone, methyl isobutyl ketone, acetone, methyl cellosolve,ethyl cellosolve, butyl cellosolve, dimethyl formamide, andtetrahydrofuran.
 11. The antiglare film according to claim 1, whereinthe b) inorganic fine particles have an average particle size of 0.4 to0.6 μm.
 12. The antiglare film according to claim 5, which has anaverage surface roughness (Ra) of 0.1 to 0.3 μm.